JPS59166229A - Method and device for removing sulfur dioxide from hot flue gas - Google Patents

Abstract

Sulfur oxides and other acid gases are removed from hot flue gases by dispersing and suspending an absorption agent and water, preferably Ca(OH)₂ suspended in water, in a rising stream of hot gas at the lower part of a reaction chamber (1), where the hot gases are subjected to a rapid reduction in velocity. Sulfur oxides and other acid gases are absorbed on and reacted with the absorption agent in the presence of evaporating water producing a dry powder which is separated from the flue gas in a particle precipitator (6,6') and partially recirculated to the reaction chamber (1).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing sulfur dioxide and other acid gases from hot flue gases, in which an absorbent and liquid water are combined in a reaction zone with a flue gas. Introduced and dispersed into the gas stream, in the reaction zone sulfur dioxide and other acid gases are absorbed by the absorbent in the presence of evaporating liquid water and react with it to become suspended in the flue gas. producing a dry powder consisting of the reacted reaction product and unreacted absorbent;
This powder is then separated from the flue gas in a separator zone,
A portion is then circulated to the reaction zone. The invention also relates to an apparatus for carrying out the method.

Various methods are known for removing sulfur dioxide and other acid gases from the flue gases of, for example, power plants and incinerator plants.

An overview of such methods is provided in U.S. Pat. No. 4,197,278.
No.

Most of these methods fall into one of the following main groups: 1) Scrubbing of the flue gas is carried out with suspended weights or solutions of argali or alkaline earth metal hydroxides or carbonates; A wet method in which the reaction mixture is taken out as a sludge.

The main advantages of this wet process are the high sulfur dioxide removal even at high sulfur dioxide concentrations in the hot flue gas and the high utilization of the absorbent. The main drawbacks are the undesirable end products produced as sludge, which presents significant disposal problems, as well as water-saturated exhaust gases that must be heated before being discharged to the atmosphere. Additionally, scrubber clogging and corrosion can lead to operational difficulties and the unusability of wet scrubbers.

11) Dry process in which the flue gas is contacted and reacted with a dry absorbent and the reaction product is removed as a dry powder.

The main advantages of the dry process are the elimination of the risk of clogging, dry solids and products as well as exhaust gases that can be easily vented to the atmosphere. However, since the reaction between gas and solid is relatively slow, the removal rate of sulfur dioxide and the utilization rate of the absorbent are low.

111) Combining the flue gas with an aqueous suspension or solution of an alkali metal or alkaline earth metal hydroxide or carbonate under conditions such that the water evaporates and the reaction products are removed as a dry powder. Below, a semi-dry method of contact.

Semi-dry processes exhibit significantly improved sulfur dioxide removal and absorbent utilization compared to dry processes, although generally not as good as those obtained by wet processes, and provide desulfurization that can be easily discharged as a final product. Provides flue gas and dry flowable solid powder.

Semi-dry methods are described in numerous patents and patent applications.

U.S. Pat. No. 98'2587 discloses the treatment of hot flue gases with an aqueous solution or slurry of alkali metal carbonates and/or bicarbonates in a spray dryer after removing fly ash from the hot flue gases. Describes so2 removal by.

GB Patent Application No. 2,201,086 describes a similar method which utilizes a cheaper absorbent, namely Ca(QH)2 suspended in water. Improved lime utilization is achieved by removing fly ash from the hot flue gas and recycling a portion of the powdered end product from the spray dryer to an aqueous slurry directed to the spray dryer. .

The viscosity of the aqueous slurry with absorbent and circulating powder, however,
Provides narrow limits on the amount of powder circulated.

In order to overcome the drawbacks of C, recycling of the dry powder by blowing it into a spray dryer was proposed in Danish patent application no. 8959/79.

The key factors describing the operating conditions of the semi-dry method are AS, T,
That is, "near the saturation temperature," defined as the reaction zone exhaust gas temperature minus the gas saturation temperature, and that the sulfur dioxide removal rate in the spray dryer and associated fabric filter is near zero AST. It is known that it increases dramatically when approaching .

However, operating spray dryers at low AST values is impractical due to the risk of "wet bottoms," i.e., the accumulation of wet or wet product on the walls and bottom of the spray dryer. do not have. This build-up of ridges is highly undesirable since it leads to tedious handling and evacuation of the solid material that settles in the spray dryer. Low AST
Values are also undesirable as they lead to inoperable conditions in the associated back-off filters.

Much effort has been made to develop a semi-dry flue gas desulphurization process using spray dryers, and this type of process is produced by the combustion of low sulfur coal and reactive alkaline fly-anoyl, i.e. spray Operating on flue gases containing fly ash, which has an alkali content that contributes to the absorption of sulfur dioxide and other acid gases in dryers, has been realized on a full scale, but flue gases especially power plants and incinerators seeks an effective commercially viable method and simple compact efficiency device for removing sulfur dioxide and other acid gases from flue gases produced in a The need exists.

Here, a small efficient device that enables a large concentration of suspended solids in the reaction zone and increases the gas-solid contact in a rational manner, and as a result, there is no risk of causing the bottom wetting phenomenon of the spray dryer and the design is not complicated. It has now been discovered that it is possible to carry out the method as defined in section 1 of this specification, which can work within the scope of the invention.

The axially introduced upward flow of hot flue gas is caused to rapidly decrease in velocity to cause boundary layer separation at the bottom of the reaction zone; absorbent, water, and powder are placed in the hot flue gas. Introduction, dispersion and suspension in the lower part of the reaction zone; removing the resulting dry powder from the upper part of the reaction zone by suspending and entraining it in the flue gas; and separating the powder from the suspension in a separate separation zone. The above is achieved by a method characterized according to the invention.

This method provides extremely close gas-solid contact for several reasons:

(1) Boundary layer separation generates a violently turbulent gas flow associated with a vigorous dispersion of absorbent and recycled powder in the lower part of the reaction zone.

(2) The material is separated by boundary layer in the lower part of the reaction zone.
) and are recycled within the reaction zone to produce particle motion upward in the center of the reaction zone and downward near the walls of the enclosed space surrounding the reaction zone.

(3) The interaction between the gravitational force acting on the suspended particles and the frictional force between the gas and the suspended particles causes further material recycling within the reaction zone.

(4) Highly turbulent gas motion results in an increase in the relative velocity between the gas and suspended particles, which is concomitant with a decrease in gas phase diffusion resistance.

The process according to the invention allows suspended solids concentrations that are significantly higher than those achieved by processes operating with downward or horizontal countercurrent gas/particle flows.

Furthermore, the large retention and rapid circulation of material in the reaction zone presents the risk of reducing porosity due to too low an AST value.

The temperature of the hot flue gas introduced into the reaction zone is generally 20
℃ or higher. When the hot flue gas is flue gas from a power plant, its temperature is generally between 110 and 250°C.
°C is typically within the range of 140 to 180 °C.

If desired, all or a portion of the fly chain may be removed prior to introducing the flue gas into the reaction zone.

The velocity of hot flue gases entering the reaction zone may vary depending on the particle loading and particle size circulating in the reaction zone. However, the velocity must be high enough to maintain particle loading in the reaction zone and prevent particles from falling from the bottom of the zone.

Although the velocity of the flue gas may be reduced, it must be sufficiently thick to ensure that it carries away particles from the top of the reaction zone, but does not ensure adequate accumulation of material in the reaction zone. must be low enough to

According to one preferred embodiment, the velocity of the hot flue gas is 1
0 to 60 m/sec, preferably 25 to 45 m/sec, to 2
~20 m/s, preferably 8-6 ηt/s,
This velocity reduction then corresponds to a velocity ratio V initial/V reduction in the range of 3 to 20, preferably 4 to 9. Adequate boundary layer separation and corresponding turbulence are achieved with the above-mentioned velocity reduction, in particular the This is ensured when the rate reduction occurs for a time within the range of 0.05 to 0.2 times the gas residence time in the reaction zone.

Such boundary layer separation is caused by the truncated conical bottom of the reaction zone having a diverging annular type, in particular wider than 12°, preferably between 2 and 120°.
, especially one with an apex angle in the range of 40 to 90°.

Apex angles greater than 120° are undesirable due to the risk of undesirable material deposition on the truncated conical bottom of the reaction zone.

The absorbent is preferably selected from each member of the group consisting of calcium and magnesium oxides and hydroxides and alkali metal oxides, hydroxides and carbonates. For economic reasons, Ca(OH)2, preferably slaked in a residence scraper, abrasive scraper or ball mill, is the preferred absorbent.

The absorbent may be introduced as a dry powder or suspended or dissolved in water, and water may be introduced separately or mixed with the absorbent.

In order to achieve high utilization of the absorbent, it is preferable to introduce the absorbent as suspended or dissolved in water.

The water or absorbent suspension in water or absorbent solution is preferably introduced into the reaction zone at a location where the flue gas velocity is high.

Preferred operating conditions are gas residence times in the reaction zone of 1 to 5 seconds, preferably 2 to 3 seconds, and material residence times in the reaction chamber of 1 to 8 minutes, preferably 3 to 5 seconds. , where the material residence time t1φ is defined as tM-HM/WM, where 111. l is the amount of material held in the reaction zone (Jcg), and W is the total amount of material injected with the solid particles present in the new absorbent flue gas Ck, 9
7 minutes).

As mentioned above, the powder consists of reaction products and unreacted absorbent. However, the flue gas entering the reaction zone is generally accompanied by fly ash, which settles into the separation zone. Fly ash may contain reactive alkali IJ'fir that can react with sulfur dioxide and other acid gases under appropriate conditions, resulting in reduced absorbent requirements.

According to one preferred embodiment, the powder circulation rate is 10 times higher than the injection rate of the absorbent and the solid particles present in the hot flue gas.
~70 times, preferably equal to 15-30 times, in which case
The sorbent injection rate is defined as the sorbent injection rate including the unreacted sorbent introduced along with the powder.

The residence time of the substances in the reaction zone is controlled by the powder circulation rate.

The average particle size of the recycled powder is preferably in the range 50 to 250 microns (/, 1). Before YA, size adjustment, e.g. sieving, etc.)i'1fl
JEGE...Dimension reduction due to fine pulverization in Zuma mill 7
This can be guaranteed by subtracting 11.

The appropriate rl A S T is obtained when water is introduced into the reaction zone in an amount intended to be 50-100% of the amount required to cool the flue gas to the adiabatic saturation temperature. .

AST is generally in the range of 0 to 40°C, preferably 5 to 40°C.
20°C, especially within the range of 8-16°C.

If desired, e.g. very low t)A S T
When operating with a reactor, the exhaust gas may be reheated, for example by blowing a portion of the hot flue gas around the reaction zone.

After leaving the reaction zone, the flue gas is dedusted, in which case the powder consisting of unreacted absorbent, reaction products and fly ash is separated out as known! They are separated in one or two stages in a separation zone.

According to one preferred embodiment, the separator G consists of two sub-zones, the first of which is a Sho 11 zone for coarse sedimentation and the second a sub-zone for fine sedimentation.

The invention also relates to a device for carrying out this method, which device has an upright axis, a downward force, an inwardly sloping annular bottom wall, and an annular bottom wall for hot flue gases in the bottom μ wall. Suspension at the top of the reaction chamber connected to a particle settler having a central inlet, a reservoir conduit for supplying absorbent, powder and water into the lower part of the reaction chamber, and a powder outlet conduit communicating with the powder supply conduit. The reaction chamber is preferably tubular in shape.G).

The extremely intimate gas-solid contact and the high concentration of solid material in the reaction zone make the use of a very compact and efficient apparatus with a simple design and therefore low (7'1) investment cost.

Adequate boundary layer separation in the lower part of the reaction zone, i.e. the annular bottom wall, and hence the corresponding turbulence generation, depends on the apex angle fJ of the annular bottom wall.
greater than 512°, preferably in the range from 40 to 9° to 12 to 120″
Guaranteed when the part is in the range from 3 to 2o, preferably from 4 to 9.

In a preferred embodiment of the process according to the invention, the absorbent is introduced into the reaction zone suspended or dissolved in water.

In this case, water and absorbent are fed through the same feed conduit.

Preferably, the water type or water and absorbent supply conduit is equipped with a Venturi injection nozzle.

According to a preferred embodiment, the apparatus is provided with means for sizing or comminution of the dry powder before it is circulated to the reaction zone.

Any known device can be used as a particle settler.

According to a preferred embodiment, the particle settler consists of a coarse particle separator, such as a cyclone separator, placed upstream of a fine particle separator, such as an electrostatic filter or a cloth filter.

The invention will now be further explained with reference to the drawing, which is a diagrammatic representation of an apparatus according to the invention.

With reference to the drawings, the apparatus comprises a tubular reaction chamber 1 complete with an annular bottom wall 2, a conduit 3 for hot flue gases, a conduit 4 for absorbent suspended or dissolved in water, and a conduit 5 for dry powder circulation.
It is equipped with The top of the reaction chamber is equipped with a dividing gate 8 which divides the powder into two streams, one that is recycled to the reaction chamber 1 and another that is disposed of as waste product as conduit 9. Separation cyclone 8 with a lower mass amount
Consists of. The exhaust gases of the separating cyclones 671) are directed via a gas outlet line 10 to an electrostatic filter 6' with a substance outlet line 7' and a gas outlet line 10'.

The fines settled in the electrostatic filter may be discharged as waste product or may be recycled in whole or in part to the reaction chamber.

If desired, the inlet conduit 4 may be replaced by two conduits, one for water and one for absorbent.

[Brief explanation of the drawing]

The drawing is a flowchart of the apparatus according to the invention. 1 Tubular reaction chamber 6 Separation cyclone 2 Tubular bottom wall 7 , material outlet 3 Conduit for hot flue gas 8
Dividing gate 4 Absorbent conduit 6' Electrostatic filter 5 Dry powder circulation conduit 7' Substance outlet tube Patent applicant F.L.Smith & Kan.
Nie Nis (4 others) Procedural amendment 1. Incident display Showa! Relationship with 2nd year patent application No. 2p, 902b case
Patent applicant's address: Potovov -f-+v, also Miss Smith p', Labor/
e nee 'nee・technical <4, agent

Claims (1)

[Claims] 1. Introducing and dispersing an absorbent and liquid water into a hot flue gas stream in a reaction zone, in the presence of liquid water in which sulfur dioxide and other acid gases are evaporated. adsorbed by and reacted with the absorbent to produce a dry powder consisting of reaction products and unreacted absorbent suspended in the flue gas;
A method for removing sulfur dioxide and other acid gases from a hot flue gas, wherein the powder is separated from the flue gas in a separation zone and partially recycled to a reaction zone; The upstream flow is subjected to a rapid velocity reduction to cause boundary layer separation in the lower part of the reaction zone, and the absorbent, water and powder are introduced, dispersed and suspended in the upstream hot flue gas at the lower part of the reaction zone, and the obtained A process characterized in that the dry powder is suspended in and entrained in the flue gas and removed from the top of the reactor, and the powder is separated from the suspension in a separate separation zone. 2. The velocity of the hot flue gas is 10-60 m/s, preferably 2.
5-45m/sec to 2-20m/sec preferably 3-6m
1 second, and the speed reduction is between 3 and 20, preferably 4
Speed ratio V first in the range of ~9. The method according to claim 1, characterized in that the method corresponds to /Viyoe. 3. The rate decrease is 0.05 to 0 of the gas residence time in the reaction zone.
3. A method according to claim 1, characterized in that the method takes place during a period of time within the range of . 4. Claims 1 to 3 characterized in that the rapid reduction in the velocity of the hot flue gas is provided by passing the hot flue gas through the frustoconical bottom of the diverging annular type of the reaction zone.
The method described in section. 5. A frusto-conical reaction zone of the diverging annular type with an apex angle in which the velocity reduction of the hot flue gas is greater than 12°, preferably in the range from 12 to 120°, in particular from 40 to 90°. 5. A method according to claim 4, characterized in that -3 is obtained by passing hot flue gases into the bottom. 6. Claims 1 to 5 characterized in that the absorbent is selected from each member of the group consisting of saponified products and hydroxides of calcium chloride and oxides, hydroxides and carbonates of alkali metals. Method described. 7. The method according to claims 1 to 6, characterized in that the absorbent is introduced as suspended or dissolved in water. 8. Gas residence time in the reaction zone is 1 to 5 seconds, preferably 2 seconds.
8. Process according to claims 1 to 7, characterized in that the residence time of the substance in the reaction chamber is 1 to 8 minutes, and the retention time of the substance in the reaction chamber is 3 to 5 minutes. 9. The powder circulation rate is 10 to 70 times, preferably 15 to 3 times, the injection rate of the absorbent and solid particles present in the hot flue gas.
Claims 1 to 8 characterized in that they are equal to 0 times
The method described in section. 10. Process according to claims 1 to 9, characterized in that the dry powder is subjected to particle size adjustment before being circulated to the reaction zone. 11. A process according to claim 10, characterized in that the dry powder is subjected to pulverization before being circulated to the reaction zone. Claims 1 to 11 characterized in that water is introduced into the reaction zone in an amount corresponding to 50 to 100% of the amount required to cool the flue gas to an adiabatic saturation temperature. The method described in section. 13. A method as claimed in claims 1 to 12, in which the rapid separation zone consists of two sub-zones, a first sub-zone for coarse sedimentation and a second sub-zone for fine sedimentation. 14. An upright shaft, an annular bottom wall sloping downward and inward, a central inlet in this bottom wall for hot flue gases, feeding absorbent, powder and water into the lower part of the reaction chamber. and a suspension outlet at the top of the reaction chamber connected to a particle settler having a powder outlet conduit communicating with the powder supply conduit. An apparatus for carrying out the method according to items 1 to 13. 15. The apex angle of the ffl-shaped bottom wall is greater than 12°C, preferably within the range of 12-120°, especially 40-90°. 15. The device according to claim 14, characterized in that: 10 L h Aj between the upper area and lower area of the annular bottom wall
16. The device according to claim 14, wherein: U/A□ is in the range of 3 to 20, preferably 4 to 9. 17. Apparatus according to claims 14 to 16, characterized in that water and absorbent are supplied through the same supply conduit. 14. The device according to claim 14, characterized in that the supply conduit force of water or water and absorbent <= Venturi injection nozzle. 19. The apparatus according to claim 14, further comprising means for subjecting the dry powder to particle size adjustment before circulating it to the reaction zone. 20. Apparatus according to claims 14 to 19, characterized in that it is provided with means for pulverizing the dry powder before circulating it into the reaction zone. 21. The device according to items 14 to 20, characterized in that the particle settler consists of a coarse particle separator arranged upstream of a fine particle separator. 22. The apparatus according to claim 21, wherein the coarse particle separator is a cyclone. 2a Claims 21 to 22, characterized in that the fine particle separator is an electrostatic filler or a cloth filler.
Equipment described in Section.